#include<stdio.h>

int main(void)
{
	int ch[26]={0};
	char input;
	
	while((input=getchar())!='\n')
	{
		if(input=='A'||input=='a')
		{
			ch[0]++;
		}
		else if(input=='B'||input=='b')
		{
			ch[1]++;
		}
		else if(input=='C'||input=='c')
		{
			ch[2]++;
		}
		else if(input=='D'||input=='d')
		{
			ch[3]++;
		}
		else if(input=='E'||input=='e')
		{
			ch[4]++;
		}
		else if(input=='F'||input=='f')
		{
			ch[5]++;
		}
		else if(input=='G'||input=='g')
		{
			ch[6]++;
		}
		else if(input=='H'||input=='h')
		{
			ch[7]++;
		}
		else if(input=='I'||input=='i')
		{
			ch[8]++;
		}
		else if(input=='J'||input=='j')
		{
			ch[9]++;
		}
		else if(input=='K'||input=='k')
		{
			ch[10]++;
		}
		else if(input=='L'||input=='l')
		{
			ch[11]++;
		}
		else if(input=='M'||input=='m')
		{
			ch[12]++;
		}
		else if(input=='N'||input=='n')
		{
			ch[13]++;
		}
		else if(input=='O'||input=='o')
		{
			ch[14]++;
		}
		else if(input=='P'||input=='p')
		{
			ch[15]++;
		}
		else if(input=='Q'||input=='q')
		{
			ch[16]++;
		}
		else if(input=='R'||input=='r')
		{
			ch[17]++;
		}
		else if(input=='S'||input=='s')
		{
			ch[18]++;
		}
		else if(input=='T'||input=='t')
		{
			ch[19]++;
		}
		else if(input=='U'||input=='u')
		{
			ch[20]++;
		}
		else if(input=='V'||input=='v')
		{
			ch[21]++;
		}
		else if(input=='W'||input=='w')
		{
			ch[22]++;
		}
		else if(input=='X'||input=='x')
		{
			ch[23]++;
		}
		else if(input=='Y'||input=='y')
		{
			ch[24]++;
		}
		else if(input=='Z'||input=='z')
		{
			ch[25]++;
		}
	}
	
	int max=0;
	for(int i=1;i<26;i++)
	{
		if(ch[i]>ch[max])
		{
			max=i;
		}
	}
	
	char output;
	output=(char)(max+97);
	
	printf("%c",output);
	
	return 0;
}
